1. Field of the Invention
The present invention relates to the field of bi-directional switches, and more specifically of bi-directional switches made in the form of vertical components in which the signal applied to the control electrode is applied with reference to the voltage of the rear surface of the component, which usually is, in vertical components, uniformly metallized.
2. Discussion of the Related Art
This type of component is described in U.S. Pat. No. 6,034,381 to Robert Pezzani, assigned to the present assignee, which is incorporated herein by reference.
FIGS. 1A, 1B, 1C reproduce FIGS. 1A, 1B, and 1C of U.S. Pat. No. 6,034,381.
The structure of FIG. 1A is formed from a lightly-doped N-type semiconductor substrate 1. This bi-directional switch comprises two vertical thyristors Th1 and Th2 in antiparallel. The anode of thyristor Th1 corresponds to a P-type layer 2 formed on the rear surface side of the substrate. Its cathode corresponds to a region 3 of the second conductivity type formed on the front surface side in a P-type well 4. The anode of thyristor Th2 corresponds to a P-type well 5 formed on the front surface side and its cathode corresponds to an N-type region 6 formed on the rear surface side in layer 2. This bi-directional switch is of the so-called well type, that is, its periphery is formed of a heavily-doped P-type wall 7 extending from the front surface side to P-type rear surface layer 2. The rear surface is coated with a metallization M1 corresponding to a first main terminal A1 of the bi-directional switch and the upper surfaces of regions 3 and 5 are coated with a second metallization M2 corresponding to the second main terminal A2 of the bi-directional switch.
The starting structure of this bi-directional switch comprises a P-type well 10 formed on the front or upper surface side in which is formed an N-type region 11. The surface of well 10 is solid with a metallization M3 connected to a gate terminal G of the bi-directional switch and the surface region 11 is connected by a metallization M4 to the upper surface of heavily-doped P-type peripheral wall 7.
The symbols of various components resulting from the shown structure have already been shown in FIG. 1A. Thus, the above-mentioned thyristors Th1 and Th2 and a transistor T1 having its base corresponding to well 10 and to gate metallization G, having its emitter corresponding to region 11 and to metallization M4 (that is, this emitter is connected by well 7 to first main rear or lower surface electrode A1 of the bi-directional switch), and having its collector corresponding to substrate 1, that is, to the anode-gate regions of thyristors Th1 and Th2, have been shown.
Currently, such a bi-directional switch is assembled so that its rear surface, generally connected to a radiator, is connected to ground and so that its front surface is connected to a voltage which is alternately positive and negative with respect to ground.
U.S. Pat. No. 6,034,381 patent shows that a bi-directional switch structure in which control electrode G is arranged on the front surface and in which the bi-directional switch is started by application on control electrode G of a signal of positive biasing with respect to the voltage of rear surface electrode A1 is obtained.
Structures of the type described in FIG. 1 have been manufactured by STMicroelectronics which has also filed several patents aiming at improvements of this structure.
However, this structure has the disadvantage that, as in the case of a conventional triac, the control is performed by current injection. Now, it is always easier to control a switch with a voltage source than with a current source.